1. Field of the Invention
The present invention is related to a system and a method thereof for backing up the data stored in a storage medium of the disk, etc. in a calculator (computer) system, and for restoring process the data if necessary.
2. Description of the Related Art
In a conventional computer system, the block information about an address etc. of the block that is being used is checked in the units of files when a file system performs a backup process. The file is read by reading out the data of the corresponding block from a disk, and the thus-read data is copied on a tape. The backup process of files was carried out by repeating the above-mentioned processes for each file.
In this method, however, since the access to a disk almost becomes a random access at the time of backing up many files, the performance of the system deteriorates.
Then, an image backup method for directly copying a plurality of blocks occupied by a file has come to be used, to economize a backup process. In this method, the computer system copies the area of blocks occupied by a file in a disk as a batch, instead of copying files selectively. Therefore, a backup process is carried out by accessing a disk one time, so that the process is economized.
However, there is a problem like the following, in the above-mentioned conventional backup method.
In the conventional image backup method, data can be copied in the units of disks, but data cannot be copied in the units of files or directories. Therefore, there is a problem that not-required data is also copied. Further, in order to restore the backed-up data, all the data should be copied and developed on a disk.
Further, the following problem occurs when a backup process is performed in a cluster system where a plurality of computers perform processes sharing a disk.
The cluster system is equipped with a file system (disk shared file system) for enabling a plurality of computers to access the shared disk simultaneously. Each computer is equipped with an area for caching the write data. Therefore, it is impossible to perform a general image backup method, since the contents of the cached write data (write cache) are not reflected on the copy only by coping the shared disk.
In a conventional computer system, an image backup method is performed during the operation of business (on-line). Therefore, when data is changed, the file system degenerates the original data which has not been changed into a different area, copies the disk, and then writes the degenerated original data over the copied data. In this way, the contents at the start point of the backup process can be determined on the backup data.
In the cluster system, however, changes made by a plurality of computers may occur almost simultaneously to the same file area. Therefore, there is a problem that a method of determining the contents at the time of starting the backup process using the original data cannot be exactly defined.
Thus, in the conventional backup method, a great amount of data in the cluster system cannot be backed-up efficiently. Therefore, an effective backup method in a cluster system has not been developed, nor exists even a method for effectively inspecting the backed-up data.